the bblog

a day in the life

I got to use my volt tester twice today, which is good, because I carry it around all day in my pocket protector; but bad, because I only use it if I'm not sure an action that I am about to take will kill me or not.

I replaced a socket in a fluoro can light; because when one of the lights burn out, in this particular type of fixture, the other socket then gets hot enough to melt to the folded tube's plastic base, but not hot enough to trip the thermal protection fuse. When the second lamp dies of accelerated old age[1], you get up there (on a 10-foot ladder, of course) to discover that the lamp can't be changed without pulling the entire fixture apart and replacing the socket.

All this means that every time I walk through the lobby I have to stare up at ceilings, hoping to spot a light out. I can't just look for dark cans, since there's two bulbs per fixture. Thanks, whoever designed this bastard. Thanks a lot.

However, replacing the socket requires shutting off power at the panel, since there's no service disconnect inside the fixture (not enough room) nor on the junction box feeding the fixture. (prohibitively expensive) However, again, this means shutting off the lights in a elevator lobby, so repairing the fixture is best done with haste.

Guess who didn't manage to repair it with haste? Me.

Vlad had been sitting on this fixture for a couple of weeks, hoping that nobody would notice that it was only holding one bulb, but eventually that bulb went out, (Two days after he retired, of course.) and I had to go up and change it. He had told me, quite clearly[2], which breaker controlled that bank of lights, so I switched it off, and screwed on the fiddly little circuit breaker lockout to ensure that nobody would flip it back on while I was at the top of a ladder[3]. Walk back out to the lobby, and discover that, nope, that's the lobby entrance lights, and hey, wow, looks like emergency exit lights start blinking when you cut off their power!

So I start flipping each breaker with the word "lights" in its tag.

Breaker 2? 6? 11? 31?

Ah, that's the ticket.

Replacing the socket was uneventful, (checking it with the volt tester to make sure it was off, returning to the topic) but turning the power back on revealed that shutting the power off at the breaker was traumatic enough to kill lights in two other fixtures.

The second time I used the volt tester was while replacing a ballast. The work order had been for a light out in Reception, and in the employee kitchen. The reception bulb was a weirdo, a BR base (incandescent floodlight form factor) compact fluorescent; (model number CF16BR30, in case you care) but in the kitchen, all four lights in the fixture were out, which is pretty damn rare. Engaging in some forensics while waiting to see if the lights would burn out[4], just working off the dates, it looked like three of the lights went out, and the fixture limped along with one for a couple of years (!) before the last one went the way of its brothers.

On my way out, I noticed some lights out in the secretarial quad, and after getting authorization,[5] I started changing them. One fixture with both lights out did have a bad ballast, (which required using the volt tester for the second time) and by the time I left I had gone through 12 tubes, about half a case.

After dropping my cart off at my office, I went down to the loading dock to get some of those chocolate wafer things, when I discovered that we were in the process of having a new vending machine delivered. The guy had just finished testing it, so I offered to be the first customer.

The vending machine had an XY (rather, YZ, since it didn't traverse the depth of the machine, ah ha ha ha) gantry, with a basket and a motor on it. The gantry would move over whatever row you selected, the motor would engage a sprocket on the front of the row, and vend whatever you selected. I put my money in, it goes through its song and dance, and nothing happens. The gantry resets and repositions itself, nothing happens. Gantry moves back to the bottom row, and now the display reads "SELECT ANOTHER PRODUCT".

Vending machine guy: Huh.
Me: At least it didn't steal my money.

Some troubleshooting later, we figure out that the row itself wasn't positioned correctly. Pop it open, fix it, now it vends correctly. Get back to my office, and the mountain dew's warm, since he had just put it in.

ALL I GOT IS PROBLEMS

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1: The typical end-of-life failure mode of a fluorescent lamp is failure to achieve discharge due to insufficient gas ionization, which is in turn due to cathode failure, high gas pressure, or incorrect gas mixture.

The electrode filaments on fluorescent tubes are great big beefy things, especially compared to the ones in incandescent bulbs, which have to be thin thanks to physics; but the therminonic emission "catalyst" (not literally a catalyst, since there are no chemical reactions occurring) coating on the cathode filaments still boil off fairly briskly. Some of these newly liberated ions will slam right into the side of the tube, producing the dark spots on the ends of old fluoro tubes, and, eventually, cracking them; allowing the atmosphere in, which both changes the composition of the gas, and raises the pressure high enough to extinguish the discharge, but the rest of the ions are lost forever.

This is bad, because the coating is what enables the discharge, and when enough of it boils off, the lamp won't light, or, in borderline cases, will only light when cold. This causes the light to turn itself on and off (the electronics will manage to light the lamp, but internal pressure will rise as the lamp warms up until the electronics can't supply enough current to sustain the discharge, at which point the lamp turns off, rinse, repeat) until the temperature cycling boils enough catalyst off to kill the lamp dead. This doesn't occur very often in fluoro tubes, since they start so quickly; but is fairly easy to observe in aged low pressure sodium bulbs; since they warm up slowly, thanks to their greater mass.

The point being, heat kills fluorescents, and keeping them hot kills them faster.

2: Lit. "Looby lights, they are controlled by breaker von on panel seeven. I am Russian, despite how bahdly Sam is mangling my accent!"

3: Being shocked at the top of a ladder usually results in death of falling off a ladder.

4: In almost every case, an entire fixture going out means the ballast's bad. So far, I've only seen this failure mode twice.

5: Some tennants like to leave fixtures half-populated, to save energy, and to confuse poor lighting fixture maintenance personnel. On these occasions, I only change lights when directly asked by the person sitting closest to the fixture.